In order to recover natural resources from underwater subterranean formations it is often necessary to perform exploration, monitoring, maintenance and construction operations on or beneath the sea floor. In relatively shallow depths these tasks can be performed by divers. However, at greater depths, and also when conditions are dangerous at shallow depths, the tasks are generally performed by robotic devices. Various types of robotic devices are known. For example, a remotely operated vehicle (ROV) is a robotic device that functions under the control of an operator via an umbilical cable that connects the ROV with a surface ship. A somewhat similar device, known as an autonomous underwater vehicle (AUV), operates according to programming, without physical connection to a surface ship. Hybrid ROVs which can operate either autonomously or via a physical connection to a surface ship are also known. Generally, ROVs are characterized by relatively limited range because of the physical connection to the surface ship. However, an ROV can operate indefinitely because energy is supplied by the surface ship. AUVs are not range-limited by a physical connection to the surface, but cannot operate indefinitely because they tend to exhaust their storage batteries quickly, necessitating frequent trips to the surface for recharging. Another difference is that ROVs exchange data and commands with the surface ship via the umbilical cable, whereas AUVs exchange data and commands via wireless communications. While ROVs, AUVs and HROVs are capable of performing tasks which cannot be practically performed in a cost-effective manner by divers, the need for a surface ship to remain on station during operations is costly. In order to reduce operational costs a system capable of performing tasks with few or no human operators near the site would be desirable.
Considerable research has been done on the problems associated with recovery of undersea resources. The following are some examples. U.S. Pat. No. 3,643,736 entitled SUB SEA PRODUCTION STATION describes production of sub sea deposits through a satellite system. The system is not configured to support autonomous operations. U.S. Pat. No. 3,454,083 entitled FAIL-SAFE SUBSEA FLUID TRANSPORTATION SYSTEM describes a system for production of fluid minerals. The system includes a product gathering network having production satellites in which the gas-oil water ratios of each well are periodically tested and the flow rates are automatically controlled. U.S. Pat. No. 6,808,021 B2, entitled SUB SEA INTERVENTION SYSTEM, describes a system that is usable within sub sea wells that extend beneath the sea floor, including a station that is located on the sea floor and an underwater vehicle. The underwater vehicle is housed in the station and is adapted to service the sub sea wells. U.S. Pat. No. 4,194,857, entitled SUB SEA STATION, describes an installation in which one or more rigid elongated base template frames are adapted to be permanently positioned on a sea floor. Each base template frame has a receptor for other modules that carry equipment in a protected manner. U.S. Pat. No. 5,069,580, entitled PAYLOAD INSTALLATION SYSTEM, describes landing and securing a payload to a subsea assembly, such as hydrocarbon recovery assembly, utilizing a surface vessel and a sub sea ROV.
Other references related to underwater operations include the following. U.S. Pat. No. 4,255,068 entitled METHOD AND DEVICE FOR UNDERSEA DRILLING, describes boring a shaft in the sea floor to form a drilling station of sufficient size to accommodate personnel and equipment. U.S. Pat. No. 5,425,599, entitled METHOD FOR REPAIRING A SUBMERGED PIPELINE, describes repairing a damaged sub sea pipeline on the sea bed by lowering pipe support frames beneath the sub sea pipeline on each side of the damaged pipeline section using ROVs and sub sea cutters. Also described is the use of airbags activated by the ROVs that hold equipment and pipes during operations in the sub sea environment. U.S. Pat. No. 3,964,264, entitled WAVE-ACTION UNDERSEA-DRILLING RIG, describes transforming energy from sub sea water motion and using that energy to drive a drilling system. The system uses turbine-blade structures positioned and shaped such that water-current force on the turbine blade structures imparts a clockwise motion to the float. U.S. Pat. No. 5,372,617, entitled HYDROGEN GENERATION BY HYDROLYSIS OF HYDRIDES FOR UNDERSEA VEHICLE FUEL CELL ENERGY SYSTEMS, describes energy generation in closed systems such as undersea vehicles. A hydrogen generator for hydrolyzing hydrides substantially at stoichiometry to provide hydrogen on demand to a fuel cell is disclosed. The generator comprises a sealable, pressurizable, thermally insulated vessel into which a hydride in granular form is loaded. Water, most of which is a byproduct of the fuel cell, is controllably introduced into the vessel for reaction with the hydride to generate hydrogen. The rate of introduction of the water is determined by the demand for hydrogen at the fuel cell. Heat transfer apparatus is disposed about the vessel to control the temperature of the reaction. A stirring mechanism is disposed in the vessel to prevent clumping of the hydride, to distribute the water to unreacted hydride, and to disperse the heat of the reaction throughout the hydride mass and thence to the heat transfer apparatus. An outlet from the vessel is provided for transfer of the generated hydrogen to the fuel cell. U.S. Pat. No. 6,856,036 B2, entitled INSTALLATION FOR HARVESTING OCEAN CURRENTS, describes harvesting kinetic energy of ocean currents in deepwater utilizing a semi-submersible platform and vertically oriented Darrieus type hydraulic turbines with funnels. The turbines are located below sea level at a distance sufficient to exclude them from being affected by wave actions. The electric power generators are located on a structure above water and transmit electric power to the shore utilizing flexible cable from semi-submersible to the sea bottom and underwater cable going to the shore, where it connected to the power distributing network.